Make sure the oil level is correct. If it is to high it will "foam up" and cause low pressure.
It will also do it if the oil is old and need to be changed.
Cali Kid made some good points too. The viscosity is the key and it sounds as if yours is breaking down.
The temp will also play a major roll in viscosity, the warmer the engine the thinner the oil gets. I had a similuar problem with my 2.5 a while back and I changed the oil and eventually all the temp sensors. Now it runs normal but I can't pinpoint the exact problem since I changed everything at once including the pressure sender.
[This message has been edited by 84Bill (edited 12-19-2003).]